The present invention relates to a method for etching composite material substrates and other substrates, and also is directed to a method for applying wear-resistant and other coatings to composite material substrates and other substrates. The present invention also relates to composite material substrates, which are comprised of particles of a hard constituent phase in a binder material phase that binds together the hard constituent particles, having wear-resistant and other coatings. The present invention finds application in any field in which it is advantageous to enhance the adhesion of a wear-resistant and other types of coatings to substrates. Examples of fields of application of the present invention include the manufacture and treatment of dies used in metal stamping, punching, threading, and blanking, and the manufacture and treatment of metal cutting inserts used in milling, turning, drilling, boring, and other metal removal operations.
Composite materials comprised of particles of a hard constituent phase and a binder phase binding the particles together are common and are referred to as xe2x80x9ccomposite materialsxe2x80x9d or xe2x80x9ccomposite substratesxe2x80x9d hereinafter. Such materials also may be referred to as xe2x80x9ccementedxe2x80x9d composite materials and include, for example, ceramics, cermets, and cemented carbides. Cemented carbides, include, for example, materials composed of a hard particulate material such as, for example, particles of one or more of tungsten carbide (WC), titanium carbide (TiC), titanium carbonitride (TiCN), tantalum carbide (TaC), tantalum nitride (TaN), niobium carbide (NbC), niobium nitride (NbN), zirconium carbide (ZrC), zirconium nitride (ZrN), hafnium carbide (HfC), and hafnium nitride (HfN) cemented together by a binder phase that is composed predominantly of one or more of cobalt, nickel, and iron.
Metal cutting inserts fabricated from composite materials are commonly used in chip cutting machining of metals in the metal machining industry. Metal cutting inserts are commonly fabricated from particles of metal carbide, usually tungsten carbide with the addition of carbides of other metals such as, for example, niobium, titanium, tantalum, and a metallic binder phase of cobalt or nickel. The carbide materials provide high strength but still may wear quickly when used in, for example, milling and other metal machining operations. By depositing a thin layer of wear-resistant material on the working surfaces of cemented carbide cutting inserts it is possible to increase the wear-resistance of the inserts without adversely affecting toughness. Commonly used wear-resistant cemented carbide insert coatings include, for example, TiC, TiN, TiCN, and Al2O3. Such wear-resistant coatings reduce the erosion and corrosion of the inserts"" binder material.
The utility of coated composite materials such as coated cemented carbides is limited by the strength of adhesion of the wear-resistant coating to the composite material. Absence of strong adhesion between wearresistant coatings and metal cutting inserts causes delamination of the coatings from the inserts, decreasing the inserts"" service life. The presence of cobalt at the inserts"" surfaces also increases the tendency of the coatings and substrates to experience delamination during use. Accordingly, it would be advantageous to provide a novel method for increasing the adhesion of wear-resistant coatings to composite materials. More broadly, it would be advantageous to enhance the adhesion of wear-resistant coatings and other types of coatings to composite material and other types of substrates.
The present invention provides a method for removing a portion of the binder phase from a substrate that is composed of at least particles of a first phase joined together by the binder phase. The present method includes the step of etching at least a portion of a surface of the substrate by contacting the surface with a gas flow that is composed of at least an etchant gas and a second gas for a time period that will allow for removal of the desired amount of binder phase. The second gas comprises one or more gases that will not react with the substrate or the removed binder material and that will not alter the oxidation state of the substrate during the etching step. Preferably, the second gas is one or more gases that will not react with the substrate or the removed portion of binder material to form deposits of a phase of WxCoyC (wherein x=3-9 and y=2-6), also referred to herein as an xcex7 (eta) phase, on the substrate.
The etchant gas used in the present method may be any gas or combination of gases that will suitable remove the desired portion of the binder phase from the substrate during the etching step. Possible etchant gases include hydrogen chloride gas, H2F2 gas, and gaseous forms of any of the Group VIIA elements. Other possible etchant gases useful in the present method will be apparent to those having ordinary skill once apprised of the present invention. The second gas may be, for example, one or more gases selected from nitrogen gas, helium gas, argon gas, and neon gas. Preferably the gas flow is applied to the substrate during the etching step by introducing a flow of the etchant gas concurrently with a flow of the second gas into a chamber containing the substrate at a pressure and temperature, and for a time, that will result in removal of the desired portion of the binder phase. In one particular application of the present method, the gas flow consists of concurrent flows of hydrogen chloride gas and nitrogen gas.
Preferably, during the etching step binder phase is removed from a surface of the substrate to a depth of between about 3 microns to about 15 microns, and more preferably to a depth of between about 4 microns to about 6 microns.
The method of the present invention preferably is applied to substrates composed of a composite material comprising particles of a hard constituent material joined together by a binder material. Examples of such composite materials include cemented carbides and cermets. Examples of the binder material of such composite materials include materials composed of one or more materials selected from cobalt, nickel, iron, elements within Group VIII of the periodic table, copper, tungsten, zinc, and rhenium. Once apprised of the details of the present invention, one of ordinary skill in the substrate coating and treatment arts will comprehend additional composite materials to which the present invention may be applied.
The present invention also is directed to a method for applying a coating to at least a portion of the surface of a substrate, preferably a composite substrate that includes hard constituent material particles joined together by a binder. The method is carried out by removing a portion of the binder from a surface of the substrate by contacting the surface with a gas flow including an etchant gas and a second gas for a period of time that will remove the desired portion of binder. The surface etching effect of the etchant gas provides an etched surface on the substrate, and the etched surface will include voids produced as the binder is etched away from between hard constituent particles The second gas is one or more gases that will not react with the substrate or the portion of the binder removed from the substrate, and that will not change the oxidation state of the substrate during the etching process, Preferably, the second gas will not react during the etching process to form eta phase within the voids etched in the substrate""s surface. In a subsequent step of the method, a coating is applied to at least a portion of the etched surface. At least a portion of the coating is deposited within at least a portion of voids on the etched surface created by removal.
Thus, the etching step of the present invention may be preceded or followed by one or more additional steps, including, for example, the step of depositing a coating on the etched surface of the substrate produced by the etching step. Because the coating infiltrates voids in the etched surface of the substrate that have been produced by removal of binder material during the etching step, the adhesion of the coating to the substrate is enhanced. Preferably, the coating is one that enhances the wear resistance of the substrate, but it also may be selected from any other conventional substrate coating. Possible wear-resistant coatings that may be applied in the coating step of the present method include those composed of, for example, one or more of TiC, TiN, TiCN, diamond, Al2O3, MT-milling coating (described in detail below), TiAlN, HfN, HfCN, HfC, ZrN, ZrC, ZrCN, BC, Ti2B, MoS, Cr3C2, CrN, CrCN, and CN.
The present invention is also directed to substrates that have been produced by the method of the present invention. For example, such substrates within the scope of the invention may have an etched surface produced by the foregoing etching step, and also may have a coating, wear-resistant or otherwise, which at least partially infiltrates voids produced in the substrate""s surface by the etching step of the invention. In particular, the present invention is directed to a substrate composed of a composite material including particles of a hard constituent material and a binder material. The substrate includes an etched surface portion having voids thereon produced by removing a portion of the binder material therefrom by contacting the surface portion with concurrent flows of at least a suitable etchant gas and a second gas. The second gas must be incapable of reacting with the substrate or the removed binder material or changing the oxidation state of the substrate during etching of the binder material. A coating may be adhered to at least a portion of the etched surface portion of the substrate, and at least a portion of the coating is deposited within at least a portion of the voids provided in the etched surface portion.
Examples of applications of the method of the present invention include the manufacture and treatment of wear resistant cutting inserts, dies, punches, and other elements used in applications such as: metal stamping, punching, threading, blanking, milling, turning, drilling, boring, and other metal removal operations; mining and oil drilling, including fabricating or treating mining and drilling bits used in long wall and coal boriig miners, tricone, percussive and rooftop drilling bits, road planing and other like applications; wood working applications, including fabricating or treating bits and blades used in sawing, planing, routing, shaping, and other woodworking applications; drawing, heading, and back extrusion, including the fabrication and treatment of punches and dies used in such applications; rod mill rolls; and high corrosion environments. An example of a specific application of the present invention is in the manufacture and treatment of items made from tungsten-based alloys containing iron, nickel, copper and/or cobalt. Such items include, for example, aircraft weights, electrical contact points, and electrodes.
The reader will appreciate the foregoing details and advantages of the present invention, as well as others, upon consideration of the following detailed description of the invention. The reader also may comprehend such additional details and advantages of the present invention upon practicing the invention.